Princeton phase inverter mod

[Wakculloch]

Some years ago there was an argument in Wireless World about the need for impedance equalizing resistors in the concertina PI, and the conclusion ( after some experimentation) was that they were not needed. The anode impedance, although theoretically higher, works at unity gain due to a large amount of negative feedback, reducing the output impedance significantly. If i remember correctly it only began to have an unbalancing affect at 10MHz or over.
Alan

[[ula58]

What about when the output tube grids are being driven hard by the PI and are taking-in grid current..then wouldn't the anode and cathode outputs of the PI have highly assymetric effects?

[Wakculloch]

Don't know.
But as a quick experiment i got a 80W, 4x 6L6 power amp that's driven by a concertina 12AU7, got it to clipping, then doubled the input drive and i couldn't see any assymetry, just crossover distortion.

[CitizenCain]

Ran across this a while back during my ramblings. I saved it for...just this occasion I guess!

[[ula58]

Cool article. I browsed through it..need to look at it more closely later and go through the math.

Thanks for posting it!

P.